Alkylenebisnaphtol derivatives and charge control agent comprising the same

ABSTRACT

The present invention provides an alkylenebisnaphthol derivative represented by formula [I]:  
                 
 
     and a salt thereof. The compound of the present invention has an excellent triboelectric charge property and useful as charge control agent for electrophotographic toners.

TECHNICAL FIELD

[0001] The present invention relates to a novel alkylenebisnaphtholderivative and a charge control agent consists of the same.

BACKGROUND ART

[0002] Developers used in electrophotographic systems such as copyingmachine include two-component developer, which comprises carrier andtoner, and single component developer, which, contains no carrier.Conventional toners used in both developers are fine particles of binderresin in which colorants, such as pigment and dye, are dispersed.

[0003] One of the important properties of the toners is triboelectricchargeability. Properties required for toners include that they cangenerate a suitable amount of positive or negative electrostatic chargeupon contacting with the carrier or charge providing device, and theamount of the charge is stable during continuous use or under an adverseenvironment. Binder resin, the main component of the toner may betriboelectrically chargeable but the amount of the generatedelectrostatic charge is not sufficient. When an image is developed witha toner containing no charge control agent, image fogging may occur tomake the resulting image unclear. In order to impart furthertriboelectric charging property, toners in general are added with acharge control agent so that the electrostatic charge is controlledsuitably.

[0004] Generally known and used charge control agent forelectrophotographic toners include positively charging agents such asnigrosin dye and quaternary ammonium salt, and negatively chargingagents such as metal containing monoazo dyes, metal-salicylic acidcomplex and copper phthalocyanine pigment.

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Although known charge control agent, especially negative chargecontrol agent has an excellent chargeability, they are not suitable formanufacturing color toner because of their color attributable to theirmain component, pigments or dyes.

[0006] Metal complex charge control agent has poor dispersibility andcompatibility with the resin and may cause inhomogeneous charge of theresulting toner. Further, the agent may easily be released from thetoner particles to stain on the development sleeve or carriers or lowerthe chargeability over continuous copying. Said problems may causereduction of resulting image density.

[0007] Further, the complex structure of a metal containing compoundlike metal complex invites high manufacturing cost. The metals likechrome may affect negatively on human body and environment. There hasbeen a demand for development of metal free charge control agent.

[0008] Japanese Patent Laid Open No. H05-11505 discloses to use acompound obtainable by linking 3-carboxy substituted 2-naphthols withalkylene such as pamo acid as a charge control agent.

[0009] The alkylenebisnaphthol derivative disclosed in this prior arthas some triboelectric charging ability but the chargeable amount islow. Therefore, said derivatives cannot be used as a charge controlagent for actual electrophotographic system.

[0010] In order to dissolve the above problems, an object of the presentinvention is to provide a novel alkylenebisnaphthol derivative which issuitably used as charge control agent for electrophotographic toner andthe like.

[0011] Further object of the present invention is to provide a novelcharge control agent having an excellent dispersibility andcompatibility with binder resins and is suitable for manufacturing colortoners, and is safe for human body as well as environment.

[0012] Still further object of the present invention is to provideelectrophotographic toner of which particles can be charged uniformlywithin a short time period and the triboelectric charging property isstable over time. Said toner can provide high quality images with highimage density and less fogging.

SOLUTION OF THE PROBLEM

[0013] The inventors have successfully synthesized novelalkylenebisnaphthol derivatives, studied their physical properties andfound that the derivatives have an excellent triboelectric chargingproperty and are useful as charge control agent for electrophotographictoners.

[0014] Accordingly, the present invention provides analkylenebisnaphthol derivative represented by the formula [I]:

[0015] wherein Y₁, Y₂, Y₁′ and Y₂′ may be same or different and each ofthem is selected from the group consisting of carboxyl group, anesterified carboxyl group, a group of —(CONH)n-X (wherein X is anoptionally branched and optionally substituted hydrocarbon group whichmay have an unsaturated bond, an optionally substituted aromatic groupand a heterocyclic group having conjugated double bonds, n is an integerof 1 or 2);

[0016] k is an integer of 1-12;

[0017] R and R′ are selected from the group consisting of hydrogen atom,an alkaline metal, an optionally branched and optionally substitutedalkyl or acyl group of 1-6 carbon atoms and a phenylalkyl group;

[0018] Q and Q′ are selected from the group consisting of an optionallybranched alkyl or alkoxy group of 1-6 carbon atoms, a halogen atom,nitro group, nitroso group, amino group and sulfo group; and

[0019] m and m′ each represents an integer of 0-3 or a salt thereof.

[0020] The present invention further provides charge control agentconsists of the above alkylenebisnaphthol derivative or its salt, and anelectrophotographic toner comprising said compound as a charge controlagent. Further more, the present invention provides use of theabove-identified alkylenebisnaphthol derivative or a salt thereof as acharge control agent.

[0021] In the above formula, examples of esterified carboxylic groupsfor Y₁, Y₂, Y₁′ and Y₂′ include an alkoxycarbonyl of 1-6 carbon atoms,such as methoxycarbonyl, ethoxycarbonyl, propyloxycarbonyl,isopropyloxycarbonyl, butoxycarbonyl, pentyloxycarbonyl andhexyloxycarbonyl; phenoxycarbonyl and phenacyloxycarbonyl. In case thegroup has an aromatic moiety, said moiety may have a substituent.

[0022] The group X may be an optionally branched and optionallysubstituted hydrocarbon group which may have an unsaturated bond,preferably an alkyl of 1-20 carbon atoms such as methyl, ethyl, propyl,butyl, pentyl, hexyl, decyl, dodecyl, lauryl and stearyl; an alkenyl of2-6 carbon atoms such as vinyl, allyl, propylenyl, butylenyl, pentylenyland hexylenyl; an optionally substituted aromatic group such as, phenyl,naphthyl, anthryl, anthraquinonyl and pyrenyl; and an optionallysubstituted heterocyclic group having conjugated double bonds such asbenzimidazolonyl, carbazolyl, pyridyl, thiazolyl, benzothiazolyl,imidazolyl, indryl, thiofuryl, phenothiazinyl, acridinyl and quinolinyl.

[0023] Examples of substituents in each definition, wherein the group isoptionally substituted, may include a halogen atom, a halogenated loweralkyl, nitro, a lower alkyl, a lower alkoxy such as methoxy, cyano,phenyl, naphthyl, phenoxy, furyl, amino, toluidylamino, triazylamino,pyrimidylamino, benzoylamino, sulfo, hydroxy, an esterified carboxylgroup such as alkoxycarbonyl and phenoxycarbonyl, amidized carboxylgroups such as phenylaminocarbonyl, alkylaminosulfonyl group and analkenyl group of 2-6 carbon atoms which may include aryl group.

[0024] When the substituent contains an aromatic ring, the compound mayfurther have one or more substituents such as a halogen atom, a loweralkyl, a lower alkoxy, phenyl, and cyano groups on said aromatic ring.

BRIEF DESCRIPTION OF DRAWINGS

[0025]FIG. 1 is an infrared absorption spectrum (KBr) of themethylenebisnaphthol derivative obtained in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] In the present specification and claims, “lower” represents agroup having 1-6 carbon atoms.

[0027] “Aromatic group” represents a 6-membered monocyclic aromaticgroup or condensed ring group consisting of up to 4 of 6-memberedaromatic rings.

[0028] “Heterocyclic group having conjugated double bonds” represents a5- or 6-membered mono-cyclic group or condensed ring group having atleast one hetero-atom selected from N, S and O and conjugated doublebonds. When it represents a condensed ring group, said group may have upto 6 rings.

[0029] In the present invention, each of the two naphthalene nuclei ofthe alkylenebisnaphthol derivative represented by formula [1] may have asubstituent of Q or Q′ respectively. Each of Q and Q′ may independentlybe selected from the group consisting of an optionally branched alkyl oralkoxy group of 1-6 carbon atoms, halogen atom, nitro, nitroso, aminoand sulfo groups.

[0030] Each of m and m′, which represents the number of the substituent,is usually 0 and may be up to 3.

[0031] The number “k” represents number of carbon atoms of the alkylenemoiety bridging the two naphthalene nuclei at 1 and 1′ positions and isan integer of 1-12. Examples of the alkylene moiety may includemethylene, ethylene, propylene, butylene, hexamethylene, octamethyleneand dodecylmethylene. Among the alkylenes, methylene and ethylene arepreferable, and methylene or the compound wherein k=1 is especiallypreferable in terms of chargeability.

[0032] R and R′ are selected from the group consisting of hydrogen atom,an alkaline metal, optionally branched and optionally substituted alkyland acyl groups of 1-6 carbon atoms and a phenylalkyl group.

[0033] According to the present invention, the salt ofalkylenebisnaphthol derivative represented by formula [I] is notspecifically limited and may preferably be alkaline metal salt such assodium or potassium salt.

[0034] The alkylenebisnaphthol derivative of the present invention isnegatively chargeable. The absolute value of the charge measured by theblow-off method under the condition specified below is high, i.e. equalto or more than 1.3 μC/g, preferably, 1.4-100 μC/g.

[0035] Examples of preferred alkylenebisnaphthol derivative of thepresent invention may include following compounds: (1)

[0036] Among the above, compound (1) is most preferable due to itsexcellent triboelectric charging property and is suitably used as acharge control agent.

[0037] The alkylenebisnaphthol derivative of the present invention maybe prepared according to the following method. The derivative of formula[I] wherein the alkylene moiety is methylene or k is 1 can be preparedby dissolving a naphthol derivative in aqueous sodium hydroxide, addingformalin to the solution and heating the mixture to 50-100° C.,preferably to 90-100° C. to condense the naphthol derivative andformalin.

[0038] When the alkylene moiety is the one other than methylene, or k is2-12, the alkylenebisnaphthol derivative of the invention may beprepared according to the following scheme:

[0039] Naphthol derivatives used as starting material for preparing thealkylenebisnaphthol derivative of the invention may be prepared by thefollowing method.

[0040] Firstly, 2-hydroxynaphthalene-3,6-dicarboxylic acid may beobtained by the method described in WO98/17621 (Japanese PatentApplication No. H10-519205). That is, by reacting potassium2-naphtholate and carbon dioxide, aciding out the reaction mixture toobtain the compound and, if desired, purifying the obtained compound.

[0041] Then, an acid chloride of thus obtained2-hydroxynaphthalene-3,6-dicarboxylic acid may be prepared by reactingthe acid with thionyl chloride or the like in a solvent such as xyleneor sulfolane in a conventional manner. The amide compound is thenobtained by treating the acid chloride with amine. Alternatively,2-hydroxynaphthalene-3,6-dicarboxylic acid may be reacted directly withan amine in the presence of phosphorus trichloride ordicyclohexylcarbodiimide to give the amide compound.

[0042] An esterified naphthol derivative may be obtained by aconventional method, such as by heating2-hydroxynaphthalene-3,6-dicarboxylic acid in an alcohol in the presenceof an acid catalyst.

[0043] Further, a naphthalene derivative wherein one of the substituentsat 3- and 6-positions is ester and the other is amide may be obtainedfrom 2-hydroxynaphthalene-3,6-dicarboxylic acid by means of the methoddescribed in WO96/32366. That is, the naphthol derivative,2-hydroxynaphthalene-3,6-dicarboxylic acid 3- or 6-mono ester and ananiline compound are reacted to effect the condensation reaction andafter that, the reaction mixture may be added with water, neutralizedand filtrated to give the desired compound.

[0044] Further, 1-halogenated naphthalene compound may be obtained bythe following method.

[0045] 2-hydroxy-3,6-dicarboxylic acid, obtainable as above, isdissolved in chloroform and dimethylsulfoxide and the mixture is cooledon ice. Halogen solution in chloroform is added dropwise thereto over 2hours at less than 50° C. The obtained mixture is stirred for one hourand then, the solution is poured into a large amount of water. Theprecipitation is collected by filtration and washed with water,dispersed in methanol, concentrated under reduced pressure at roomtemperature and dried to give the desired 1-halogenated naphtholderivative.

[0046] The alkylenebisnaphthol derivative of the present invention has ahigh chargeability, high compatibility with resins, and therefore, canbe dispersed uniformly in the resin. In addition, the compound has onlyslight color or is almost colorless, and therefore, the compound willnot interfere with the color of the colorant.

[0047] Further, the alkylenebisnaphthol derivative of the presentinvention can be synthesized by a simple process and therefore, with lowcost. No metal is contained and therefore, the derivative is safe forhuman being and environment. Accordingly, the novel compound of thepresent invention can preferably be used as a charge control agent,especially negatively chargeable charge control agent forelectrophotographic toners. By using the compound of the presentinvention, electrophotographic toners with excellent properties can beprovided.

[0048] Electrophotographic toners comprising the alkylenebisnaphtholderivative of the present invention as a charge control agent aredescribed below. In general, toners for electrophotography are preparedby dispersing additives such as colorant and charge control agent in thebinder resin. The toner of the present invention may be manufactured ina manner similar to the conventional toners using the above describedalkylenebisnaphthol derivative as a charge control agent.

[0049] In manufacturing toner of the present invention, binder resinsmay be any of those used for conventional electrophotographic toners,for example, polystyrenes, polyacrylenes, styrene-acrylic copolymers,styrene-methacrylate copolymers, styrene-propylene copolymers,styrene-butadiene copolymers, styrene-maleic acid copolymers, olefinresins, polyesters, epoxy resins polyurethanes and polyvinyl butyrals.Those resins may be used alone or two or more of them may be used incombination.

[0050] Any of the colorants used for manufacturing conventionalelectrophotographic toners may preferably be used for the toner of thepresent invention. Examples of said colorants include carbon black, lampblack, iron black, cobalt blue, nigrosin dye, aniline blue,phthalocyanine blue, phthalocyanine green, hansa yellow, chrome yellow,rose bengal, triaryl methane dyes and monoazo and bisazo dyes orpigments. The colorants may be selected based on the desired color ofthe resulting toner.

[0051] The amount of the colorant per 100 parts by weight of the binderresin may preferably be 1-20 parts and preferably 2-10 parts by weight.

[0052] The toner of the present invention comprises alkylenebisnaphtholderivative of formula [I] as a charge control agent. In order to obtaintoners with sufficient chargeability and good quality, the amount of thealkylenebisnaphthol derivative of formula [I] per 100 parts by weight ofthe binder resin may be 0.1-10, and more preferably, 0.1-5 parts byweight.

[0053] The electrophotographic toner of the present invention maycomprise other known charge control agents such as metal containingmonoazo dyes, metal-salicylic acid complexes and copper phthalocyaninepigments in combination with the alkylenebisnaphthol derivative of thepresent invention.

[0054] The toner of the present invention may further comprise additivesused for manufacturing conventional toners, for example, mold-releasingagent, external additives and the like. Low molecular weight olefinpolymer may preferably be used as mold-releasing agent. The externaladditives are those added to improve flow property, cleaning propertyand shelf stability of the toner. Examples of the external additives mayinclude inorganic fine particles such as silica, alumina and titaniumoxide.

[0055] The particle size of the toner is not particularly limited andpreferably, equal to or less than 20 μm, more preferably, equal to orless than 10 μm.

[0056] The electrophotographic toner of the present invention may bemanufactured by any known method. For example, but not limited to, themethod wherein the above described ingredients are mixed uniformly bymeans of dry blender, Henschel mixer, ball mill or the like; theobtained mixture is melt and kneaded by means of a kneading machine suchas Banbury mixer, roll extruder and single- or twin-axis extruderkneader; the uniformly kneaded matter is cooled and pulverized; and ifdesired, classified, and then added with the external additives to givethe toner may be employed. Alternatively, any of known methods such aspolymerizing method, microcapsule polymerizing method and spray drymethod may be employed for the manufacture.

[0057] The charge control agent of the present invention exhibits goodcompatibility with resins and therefore, the agent can be admixed intothe binder resin together with the other ingredients to give uniformlyand stably chargeable toners. The charge control agent of the presentinvention may be fixed or embedded on the surface or the area adjacentto the surface of the fine particles comprising binder resin and acolorant by means of a known method using mechanical impact.

[0058] The electrophotographic toner of the present invention comprisingthe alkylenebisnaphthol derivative of the present invention as a chargecontrol agent can be uniformly charged within a short time period andthe triboelectric charging property is stable over time. Accordingly, byusing the toner of the invention, high quality images with high imagedensity and less fogging can be provided. Further, stain of thedevelopment sleeves and carriers with the charge control agent iseffectively reduced and therefore, the toner can provide high densityimages stably over continuous copying.

[0059] Further more, the alkylenebisnaphthol derivative of the presentinvention has least impact on the resulting color and therefore, usefulfor manufacturing color toners.

EXAMPLES

[0060] The present invention is further described in reference to thefollowing examples. The following examples are intended to illustratethe invention and are not to be construed to limit the scope of theinvention.

Example 1

[0061] 1,1-methylenebis(2-hydroxynaphthalene-3,6-dicarboxylic acid)

[0062] 2-hydroxynaphthalene-3,6-dicarboxylic acid 9.3 g was dissolved in10% aqueous sodium hydroxide 40 g and the solution was heated to 90° C.37% Aqueous formalin 4.2 g was added thereto and the mixture was reactedfor 2 hours at 95° C. After that, the reaction mixture was treated withcarbon at 50° C. and adjusted to pH 3 with 10% aqueous hydrochloride.The precipitates were collected by filtration, washed well with waterand methanol, and dried to give pale yellow powder 7.3 g (decompositionpoint: 294.3° C.). The infrared absorption spectrum (KBr) of thecompound is shown in FIG. 1.

[0063] The triboelectric charging property of thus obtained1,1′-methylenebis(2-hydroxynaphthalene-3,6-dicarboxylic acid) wasdetermined by means of blow-off powder electrostatic charge tester(#TB200, Toshiba Chemical Corp, Tokyo, Japan) using metal mesh of200-mesh (75 μm) under the condition shown below. The resultingtriboelectric charge was −7.89 μC/g.

[0064] Measurement Conditions:

[0065] Temperature: 20° C.

[0066] Relative Humidity: 20%

[0067] Blow gas: N₂, 1.0 Kg/cm²

[0068] Blow-off time: 60 seconds

Examples 2-4

[0069] Methylenebisnaphthol derivatives were synthesized in the similarmanner as example 1 except for using the materials shown in table 1below instead of 2-hydroxynaphthalene-3,6-dicarboxylic acid. Thetriboelectric charging property and decomposition point of thus obtainedcompound were determined. TABLE 1 tribo- decompo- electric sition Exmethylenebisnaphthol charge point No material derivatives μC/g ° C. 2

−1.45 315.1 3

−1.53 322.8 4

−1.38 306.4

Examples 5-7

[0070] Methylenebisnaphthol derivatives are synthesized in the samemanner as example 1 except for using the materials shown in table 2below instead of 2-hydroxynaphthalene-3,6-dicarboxylic acid. Thedecomposition point of thus obtained compound was determined. TABLE 2 ExMethylenebisnaphthol decomposition No material derivatives point ° C. 5

347.6 6

300.2 7

339.8

Comparative Examples 1-3

[0071] Methylenebisnaphthol derivatives were synthesized in the samemanner as example 1 except for using the materials shown in table 3below instead of 2-hydroxynaphthalene-3,6-dicarboxylic acid. Thetriboelectric charging property and decomposition point of thus obtainedcompound were determined. TABLE 3 tribo- decompo- electric sition Compmethylenebisnaphthol charge point Ex material derivative μC/g ° C. 1

−1.19 312.9 2

−0.76 325.0 3

−0.17 234.0

[0072] Examples of toners are shown below. In the followingcompositions, “part(s)” means “part(s) by weight”.

[0073] Black Toner

[0074] Styrene-acrylic resin 100 parts, carbon black 6 parts and thecompound of Example 1 2 parts are preliminary mixed uniformly with theball mill, and then, the mixture is molten and kneaded with thedispersion kneader. The kneaded mixture is roughly crushed with thevibration mill and further pulverized with the jet mill to give theblack toner.

[0075] Color Toner (Cyan)

[0076] Color toner (cyan) may be prepared in a manner similar to theblack toner except for using polyester resin instead of styrene-acrylicresin and phthalocyanine blue instead of carbon black.

[0077] Color Toner (Yellow)

[0078] Color toner (yellow) may be prepared in a manner similar to theblack toner except for using polyester resin instead of styrene-acrylicresin and hansa yellow instead of carbon black.

[0079] Color Toner (Magenta)

[0080] Color toner (magenta) may be prepared in a manner similar to theblack toner except for using polyester resin instead of styrene-acrylicresin and rose bengal instead of carbon black.

1. An alkylenebisnaphthol derivative represented by formula [I]:

wherein Y₁, Y₂, Y₁′ and Y₂′ may be same or different and each of them isselected from the group consisting of a carboxyl group, an esterifiedcarboxyl group, a group of —(CONH)n-X (wherein X is an optionallybranched and optionally substituted hydrocarbon group which may have anunsaturated bond, an optionally substituted aromatic group and aheterocyclic group having conjugated double bonds, n is an integer of 1or 2); k is an integer of 1-12; R and R′ are selected from the groupconsisting of hydrogen atom, an alkaline metal, an optionally branchedand optionally substituted alkyl or acyl group of 1-6 carbon atoms and aphenylalkyl group; Q and Q′ are selected from the group consisting of anoptionally branched alkyl or alkoxy group of 1-6 carbon atoms, a halogenatom, nitro group, nitroso group, amino group and sulfo group; and m andm′ each represents an integer of 0-3 or a salt thereof.
 2. Thealkylenebisnaphthol derivative or a salt thereof of claim 1, wherein kis
 1. 3. The alkylenebisnaphthol derivative or a salt thereof of claim1, wherein said derivative is negatively chargeable and the absolutevalue of the triboelectric charge is equal to or greater than 1.3 μC/g.4. A charge control agent consisting of an alkylenebisnaphtholderivative represented by formula [I]:

wherein Y₁, Y₂, Y₁′, Y₂′, k, R, R′, Q, Q′, m and m′ are as defined inclaim 1 or a salt thereof.
 5. Use of an alkylenebisnaphthol derivativerepresented by formula [I]:

wherein Y₁, Y₂, Y₁′, Y₂′, k, R, R′, Q, Q′, m and m′ are as defined inclaim 1, or a salt thereof as a charge control agent.
 6. Anelectrophotographic toner, comprising at least a binder resin, acolorant and an alkylenebisnaphthol derivative of formula [I]:

wherein Y₁, Y₂, Y₁′, Y₂′, k, R, R′, Q, Q′, m and m′ are as defined inclaim 1, or a salt thereof.